Mercury, atomic isomer

It is noteworthy that a complete stereoselectivity toward the cA-isomer, which is opposite to that found in aminomercuration of the same dienes173 characterizes these reactions. The following mechanism has therefore been proposed to rationalize the stereochemical behavior. After the addition to one of the double bonds, the electron pair of the nitrogen should interact with the mercury atom. In a second step, another mercury(II) ion from an additional molecule of mercury(II) nitrate is similarly complexed by the electrons of the nitrogen atom, requiring an approach from that same side and resulting in a cis... 

The preliminary electronic interaction seems to be required since, if the first mercury atom is absent, a trans addition takes place. Furthermore, a possible important role of the basicity of the nitrogen has been underlined taking into account that aminomercuration of 1,4- and 1,5-hexadienes with aromatic amines leads mainly to the trans isomer. 

Mercuration of quinoline N-oxide in acetic acid or perchloric acid gives the 8-mercurio-chloride (26) as the main product and small amounts of the 3-, 5-, 6- and 7-isomers. In the absence of solvent mercury(II) sulfate gives all the possible isomers although the total yield is poor. 6-Methylquinoline N-oxide gives the 8-substituted derivative (27). The preferential 8-orientation is accounted for in terms of preliminary coordination of the mercury atom at the oxygen of the N-oxide. When the 8-position is blocked, as in 8-bromoquinoline N-oxide, mercuration is reported to occur at the 4-position (55YZ490, 69CPB906). 

In the last example, we consider the doubly charged tetramercury cluster Hg in both cyclic and linear shapes [69]. The computations showed that the cyclic isomer of Hg4 has a perfect symmetry (Figme 14.14). Each mercury atom contributes... 

In most cases, it has been proposed that the cationic intermediate resulting from electrophilic attack by the mercuric ion is, in fact, a mercurinium species 109 in which the mercury cation is unsymmetrically coordinated to the two alkynyl carbon atoms. Hence, these reactions typically afford Markovnikov products. In the presence of excess Hg(OAc)2, nucleophilic attack of the mercurinium intermediate is intermolecular and occurs in an anti-fashion leading to the (ft)-isomer. When no excess of Hg(OAc)2 is present, nucleophilic attack of the mercurinium intermediate is intramolecular and occurs in a ry -fashion leading to the (Z)-isomer.1... 

The reaction of [PPN][Au2 CH2P(S)Ph2 2] with HgCl2, followed by T1PF6 treatment, resulted in a rearrangement of the Au-C bonds and compound 6 was isolated. It is an isomer of compound 5 in the cation of which both gold and mercury are linearly coordinated by a carbon and a sulfur atom. The isomers 5 and 6 do not interconvert under reflux inTHF [36]. The transannular gold-mercury distance in the cation of 6 [2.989(1) A] is about 0.1 A shortest than in the cations containing the... 

By far the greatest number of photochromatic compounds, however, are organic. As in the inorganic compound mercury dithizon-ate, photochromism in organic compounds occurs when one form of a compound is exposed to light, which converts the compound to an isomer of a different color. In most such instances, the two isomers differ in that one is a closed form of the isomer and the other is an open form. In some cases, however, the two isomers differ in that one occurs in a trans form and the other in a cis form. Trans and cis isomers are forms of a compound in which two constituent atoms or groups are located on opposite or the same side of a molecule, respectively. 

The trimetallic complex [Fe3(CO)8(p-PPh)2(PF3)] has been obtained from the corresponding [Fe3(CO)8(p-PPh)2(MeCN)J compound by displacement of MeCN (method G). The structure, which is based on a square-pyramidal array of three iron and two phosphorus atoms, consists of isomers whose interconversion has been studied by variable-temperature 19F and 31P NMR spectroscopy. A trimetallic PF3 complex containing mercury bonded to two metals results from the reactions... 

Very little is known regarding the nature of the electronic state responsible for the decomposition of other ketones. The low quenching efficiencies observed in the photolysis of 2-hexanone may be interpreted by the short-life-time of the triplet state of 2-hexanone. The similar distribution of the butene isomers found in the photolysis of 4-methyl 2-hexanone at 2537 A and in its mercury-sensitized decomposition, indicates the important role played by the triplet state in reaction II even at short wavelengths. Finally, it is to be mentioned that the presence of secondary H atoms in the y position seems to enhance the contribution of the excited singlet state to the decomposition step II. 

The more substituted systems rearranged simply on warming in 2,2,2-trifluoroethanol but the assistance of silver(I) or mercury(II) salts was necessary to achieve cyclization of the less highly substituted compounds. In the formation of 3-(phenylmethylene)tetrahydropyran, cyclization occurred at the less highly substituted cyclopropane carbon atom, in the disrotatory mode, to give the product as a single isomer. ... 

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